Observations of magnetic and structural ordering inTbH2+xcompounds through electrical resistivity measurements

We present detailed resistivity measurements ρ(T) in the magnetically ordered state of ${\mathrm{TbH}}_{2+\mathrm{x}}$. Three types of behavior are observed: (i) for x≃0, we find a classical antiferromagnetic transition with a well-defined drop of the spin-disorder resistivity below $T_N$≃18 K; (ii) for x>0, the total resistivity ρ(T) goes progressively through a minimum and a maximum with decreasing temperature, indicating an incommensurate type of ordering which starts at temperatures above $T_N$; (iii) for x≥0.15 and for samples presenting a structural transition within the H sublattice, we observe a sharp transition at 38 K, with a smoother minimum at about 55 K. These results can be at- tributed to modifications of the electronic structure and of the mean free path with x, and to the existence of uniaxial crystalline field effects related to structural short-range and long-range order in the H sublattice.